This invention relates to new and useful improvements in gate valves of the type having a wear and corrosion resistant lining.
Gate valves are in common use for controlling flow media such as slurries and corrosive fluids. These valve have a flow passage therein controlled by a plate-like gate slidable in a recess in the liner. Gate valves often are used to control flow of slurries or corrosive fluids containing abrasive solids and are lined with a resilient, tough wearing and corrosion resistant material such as polyurethane or polyethylene. Low pressure gate valves are readily sealed, namely, by the closing thrust of the gate and by a sealed fit in liners or seals. High pressure valves on the other hand create more problems in that sealing is more difficult and high pressures can bend the gate at its lower end. When there is side backing support for the gate to reinforce it against high pressure, a large amount of friction may exist for opening and closing he gate. Also, side supports on any gate, whether in low or high pressure systems, create pockets or obstructions which can hinder the free flow of material. For best performance and all around functioning, it is desired (1) that the structure of the gate valve when open provide no obstruction through the flow passage so that there will be efficient flow and minimum wear; (2) that the gate have a good sealing function in the valve body for both low and high pressure flow; (3) that the gate have backing support at its lower portion so that high pressure conditions in the fluid, preferably from either direction, do not damage the gate; and (4) that the friction of gate movement be low enough so that the gate can be readily opened and closed. It is also desired that particles in the fluid do not gather in the valve to the extent that they jam the gate. This combination of structural features has not been fully achieved heretofore.
Considering prior patented structures, for example, reference is made to U.S. Pat. Nos. 2,851,051 and 4,603,864. Although no doubt effective to an extent in their operation, portions of the gate seal form obstructions in the flow passage and thus minimize efficient fluid flow. Also, heavy particles can jam at the seal and abrasive slurries will cause undue wear. Structure shown in U.S. Pat. No. 4,112,969, has a flow passage in the body member which is unobstructed, but use with high presure is not possible because there is no backing support for the gate at a lower portion thereof and the gate will warp under such pressure.
U.S. Pat. Nos. 2,669,416 and 4,201,365 provide backing and/or sealing support for the gate but in order to do this such support or sealing means form an obstruction in the flow passage flow. Also, backing support in these patented structures is only effective in one direction of flow. U.S. Pat. Nos. 3,784,158, 3,897,043, 4,377,274, 4,522,224, and 4,693,447 employ gate valve seals that use a groove associated with the sealing end of the gate for accomplishing the sealing function. This type of grooved structure has the disadvantage of allowing particles to collect therein and hinder opening and closing of the gate and proper seating.